tools/testing/selftests/proc/proc-2-is-kthread.c

   1 /*
   2  * Copyright (c) 2024 Alexey Dobriyan <adobriyan@gmail.com>
   3  *
   4  * Permission to use, copy, modify, and distribute this software for any
   5  * purpose with or without fee is hereby granted, provided that the above
   6  * copyright notice and this permission notice appear in all copies.
   7  *
   8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15  */
  16 /* Test that kernel thread is reported as such. */
  17 #undef NDEBUG
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <fcntl.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23
  24 int main(void)
  25 {
  26         /*
  27          * The following solutions don't really work:
  28          *
  29          * 1) jit kernel module which creates kernel thread:
  30          * test becomes arch-specific,
  31          * problems with mandatory module signing,
  32          * problems with lockdown mode,
  33          * doesn't work with CONFIG_MODULES=n at all,
  34          * kthread creation API is formally unstable internal kernel API,
  35          * need a mechanism to report test kernel thread's PID back,
  36          *
  37          * 2) ksoftirqd/0 and kswapd0 look like stable enough kernel threads,
  38          * but their PIDs are unstable.
  39          *
  40          * Check against kthreadd which always seem to exist under pid 2.
  41          */
  42         int fd = open("/proc/2/status", O_RDONLY);
  43         assert(fd >= 0);
  44
  45         char buf[4096];
  46         ssize_t rv = read(fd, buf, sizeof(buf));
  47         assert(0 <= rv && rv < sizeof(buf));
  48         buf[rv] = '\0';
  49
  50         assert(strstr(buf, "Kthread:\t1\n"));
  51
  52         return 0;
  53 }